What Is a Foot Valve? Pump Suction
A foot valve is a type of check valve installed at the bottom end of a pump suction line, submerged in the liquid source (tank, sump, or well). Its primary function is to maintain prime in centrifugal pumps by preventing the liquid column in the suction pipe from draining back into the source when the pump shuts down. Without a foot valve, the pump would lose prime and require manual repriming before each restart.
How a Foot Valve Works
The valve contains a hinged disc or poppet that opens when the pump creates suction (flow upward) and closes by gravity and backflow pressure when the pump stops. A strainer screen is typically integrated into the body to prevent debris from entering the suction line and damaging the pump impeller. The valve is sized to match the suction pipe diameter to minimize friction losses.
| Parameter | Details |
|---|---|
| Function | Maintain pump prime, prevent backflow |
| Location | Bottom of suction line, submerged in liquid |
| Disc type | Swing (hinged), poppet (lift), or spring-loaded |
| Built-in strainer | Yes (perforated screen or mesh basket) |
| Sizes | 1 in to 24 in |
| Pressure class | Class 125/150 (low-pressure suction service) |
| Body materials | Cast iron, ductile iron, bronze, 316 stainless steel, PVC |
| End connections | Flanged (ASME B16.5), threaded (NPT/BSP), or plain end |
| Seal | Rubber, PTFE, or metal seat |
| Standards | API 594, MSS SP-80, BS 5153 |
Foot Valve vs Standard Check Valve
| Feature | Foot Valve | Standard Check Valve |
|---|---|---|
| Location | Submerged at suction pipe bottom | Anywhere in the line |
| Strainer | Integrated | Not included |
| Primary purpose | Maintain pump prime | Prevent backflow |
| Flow direction | Vertical (upward only) | Horizontal or vertical |
| Pressure class | Low (suction side) | Any rating |
| Maintenance access | Difficult (submerged) | Accessible in-line |
Selection Considerations
The valve material must be compatible with the pumped fluid. Bronze or stainless steel is preferred for water supply and chemical applications; cast iron is common for non-corrosive industrial water. The strainer mesh opening should be fine enough to protect the pump but coarse enough to avoid clogging. Regular cleaning of the strainer is required, particularly in dirty water or open-sump applications.
Foot valves are commonly used with centrifugal pumps in oil and gas facilities, water treatment, irrigation, and fire protection systems. For high-reliability installations, designers may prefer a suction-line check valve combined with a separate strainer for easier maintenance access.
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